The present invention relates to optical sorting apparatus and methods for sorting individual objects such as beans, nuts, seeds, or other agricultural products to detect optically discernible defects in the objects.
Presently, various apparatus exist for carrying out optical sorting of objects. Generally, these apparatus include a feeding device which separates a quantity of objects into individual streams of moving objects. The object streams pass through viewing zones where the individual objects are illuminated. Light reflected from each of the illuminated objects is collected by one or more photo-amplifiers and analyzed to determine if the object is acceptable.
When sorting is based on color, at least two photoamplifiers are typically provided. Each photo-amplifier responds to a region of the light frequency spectrum. The photo-amplifiers produce electric signals which are proportional to the intensity of the light detected. The electric signals are processed by an electronic circuit which determines whether a given object is acceptable based on its electric signal. The electronic circuit activates a rejection mechanism that separates an unacceptable object from the object stream when the unacceptable object is detected.
A number of problems and disadvantages exist with known sorting apparatus. Typically they use painted backgrounds as color references for optically sorting objects. For example, a photo-amplifier concurrently receives light reflected from an object being viewed and a painted background with the same color as an acceptable object of the type being viewed. If the light reflected from the object being viewed does not closely match the light reflected from the painted background with the same color as an acceptable object of that type, the electric signal produced is analyzed as unacceptable and the object is rejected.
The color reference provided by a painted background must typically match the acceptable color as predetermined for a particular type of object to within a 1 to 1.5% tolerance. Consequently, numerous backgrounds are necessary given the wide variation in colors for different types of objects. For example, when known sorting devices are used to sort peanuts and then coffee beans a change of painted backgrounds is required. Likewise, to switch from sorting one grade of coffee bean to another a change of backgrounds is required. Further, determining the appropriate color reference for a particular type of object may require extensive research.
Painted backgrounds in known sorting apparatus deteriorate and get dirty thereby causing problems. The color of a deteriorated or dirty background frequently does not match the color reference for acceptable objects that it was designed to match. Consequently, when acceptable objects are optically compared to deteriorated or dirty backgrounds the acceptable objects may be rejected.
Viewing heads for known optical sorting apparatus are relatively bulky for the viewing area they provide. For example, a viewing head with a 30 cm outside diameter may provide only a 5 cm viewing zone. The diameter disparity is necessary to allow the viewing head to accommodate lamps for illuminating the viewing zone as well as space intensive equipment such as lenses, photo-amplifiers, and filters. Lamps used in known viewing heads also generate a substantial amount of heat which affects response characteristics of the photo-amplifiers and causes deterioration of the backgrounds. The amount and proximity of equipment provided in known viewing heads creates additional problems such as limiting the number of viewing channels available due to a lack of space, and causing electrical interference in the photo-amplifier circuits due to the lamp power-circuits.
Known optical sorting apparatus also have the problem of rejecting an acceptable object when defects are detected in the proximate end of a nearby, unacceptable object. This problem typically occurs in two ways: First, imprecision in the timing mechanism may cause the rejection of an acceptable object passing through the viewing zone either immediately before, or after, the defective object. Second, known viewing mechanisms may associate a defect at either end of an unacceptable object with both the unacceptable object and an acceptable object passing through the viewing zone either immediately before, or after, the unacceptable object. These problems particularly occur when the objects being sorted are bunched together in the object stream--i.e., when the spacing between objects is small.
Faulty alignment of viewing heads and viewing assemblies in known sorting apparatus also leads to incorrect sorting operations. Two forms of alignment are necessary for proper sorting. First, the viewing head is aligned with respect to the object stream. This may need to be done on a regular basis, particularly when the device is used to sort a wide range of objects. Second, each viewing assembly is separately adjusted with respect to the viewing head and object stream. The viewing assemblies ideally are adjusted to form a flat circle around the object stream. This insures that all views are synchronized, resulting in actuation of the rejection mechanism at substantially the same time regardless of which viewing assembly actually sees the defect in an unacceptable object.
Rejection of acceptable objects as a result of dirt clouding the windows and lenses of viewing assemblies has also been a problem associated with known optical sorting apparatus. Consequently, the windows and lenses of the viewing assemblies must either be frequently cleaned or the electronic detector circuit must be regularly adjusted to compensate for the loss in photo-amplifier signal strength due to the dirty windows and lenses. Otherwise, an acceptable object may be rejected due to loss in photo-amplifier signal strength.